1. Field of the Invention
This invention relates to the provision of coated abrasives which provide a novel combination of high productivity with economy and rapidity of manufacture. In the prior art, the vast majority of coated abrasives have been made with adhesives of animal glue or of synthetic resins, usually thermosetting resins such as urea-formaldehyde or phenol-formaldehyde. Animal glue has a rapid gelling quality which permits the rapid manufacture of coated abrasives which utilize it as the only adhesive, but the grinding or finishing performance of the coated abrasives made with it is not usually as good as of those made with thermosetting resin adhesives. The latter, however, often require several hours of cure before reaching their ultimate strength. This curing time requirement slows the manufacture of the products.
In one of its embodiments, this invention relates particularly to coated abrasive products adapted to the operations of lens fining. This is an established term of ophthalmic art. Further descriptions of the the fining process and of suitable machinery for accomplishing it are readily available in prior patents, e.g., U.S. Pat. Nos. 4,320,599 to Hill et al. and 3,732,647 to Stith, the entire specifications of which patents are hereby incorporated herein by reference. The particular field of this embodiment of the present invention is the provision of an advantageous type of lapping tool such as is shown as item L of the drawings of the Stith patent. The lapping surface 78 of FIG. 2 of the Stith patent may be provided, as has been known, by a suitable coated abrasive material consisting of abrasive grains adhered to a flexible backing, which in turn is supported by the structure of the lap L in Stith FIG. 2.
In another of its embodiments, this invention relates to coated abrasives particularly suited to crankshaft lapping in the manufacture of engines. In still another embodiment, this invention relates to coated abrasives especially suited to the finishing of primer coats and other synthetic surface coatings used for final surface finishing of articles of manufacture made of metal, particularly automobile bodies.
This invention in most of its embodiments also relates to the field of adhesives curable by exposure to ultraviolet (hereinafter UV) light.
2. Description of the Prior Art
The use of adhesives capable of rapid cure under the influence of actinic radiation, particularly UV light, has provided attractive combinations of manufacturing speed and adhesive quality in many coating operations, including a wide variety of decorative surface coating, in which relatively thin and transparent adhesive coatings are adequate. Nevertheless, the use of UV cured coating materials for coated abrasives has been very limited. It appears to have been generally believed that the relatively thick layers of adhesives typically required for coated abrasives would be very difficult or impossible to cure with UV light, because of the limited depth of penetration of such light into most appropriate adhesive formulations. Therefore, most of the workers in the field are believed to have concentrated instead on electron beam curing, as exemplified by U. K. Patent Application 2,087,263, published 26 May 1982. Electron beam curing, while effective, requires significantly greater capital investment than curing with UV light and presents a more serious potential hazard to personnel.
The only published instance of a coated abrasive prepared by UV curing known to us is Japanese Laid-Open Application No. 119491/1978, dated 18 Oct. 1978. This document indicated that the presence of an isocyanate compound in the adhesive is important for success with UV light initiated cure of adhesives for coated abrasives. Furthermore, although it was generally asserted in this Japanese publication that all the formulations disclosed therein are suitable for cure by UV light as well as electron beam curing, only one of the sixteen specific examples actually used UV light, and the adhesive used for this example contained no triacrylated monomers and only a little diacrylated monomer, with the bulk of the adhesive being non-acrylic types of polymerizable unsaturated esters and styrene. The main goal of the art described in this publication appeared to be the use of lower than normal energy electron beams and relatively inexpensive adhesives.
Both the above Japanese reference and a more general teaching by Dixon in U.S. Pat. No. 4,222,835, not referring specifically to coated abrasives, have taught some advantages of using thermal initiators in adhesive formulations intended for radiation-initiated cure.
A waterproof paper coated abrasive with fast curing adhesives was disclosed in U.S. Pat. No. 4,047,903 to Hesse et al., but this product was cured by electron beam radiation only.
U.S. Pat. Nos. 3,844,916, 3,914,165, and 3,925,349 to Gaske teach the use of adducts of acrylates with dibutyl amine and diethyl amine in adhesive formulations suitable for UV light initiated cure generally. These references teach nothing explicitly related to coated abrasives and advance, as the principal advantage of using the amine adducts, counteracting the normal inhibitory effect of atmospheric oxygen on the cure.
U.S. Pat. Nos. 4,391,947 to Sassano and 4,414,367 to Gardner teach various curable coating and molding compositions which include esters of iso-phthalic acid. These compositions are different from those disclosed herein, particularly because of the presence of substantial amounts of styrene or similar copolymerizable monomers, and the Sassano and Gardner references do not teach or suggest any utility of their compositions for coated abrasives.